Best Humidity-sensor and calibrating it ?

Hi,
Two questions.
One thing I wonder is how... to check the outcome of a humidity sensor ?
I could hold one in a freezer (0%) or damped box (90% +), but how can I actually check
when a sensor displays 50% air-humidity from a sensor it also agrees with reality ?
Calibrating a PH-sensor is relative simple


2nd one, more electronics related.
I bought five DHT-11 humidity/temperature sensors on Ebay for a bargain. I'm slowly automating my indoor garden using micro controllers. Max difference in temperature 3 degrees (C) and I'm using far more accurate sensors for that. Unfortunately 1 out of 5 sensors never displays a humidity above 30% and the others work better but differ up to 13% from each other. Repairing 'm using the info of the data-sheet didn't help much.

I know other/better ones exist, DHT-22, Sensirion, Honeywell and others, but I would like to hear from others what their experiences are, before buying another piece of crap.


Best wishes,
Bart.

Bump... Anyone ?

ok first humidity isnt a big deal. it is, but it isnt. for clones, you want it high 90%ish, veg around 50-60, and flower you want less. the main thing reason you cut back on humidity is to prevent the environment from being too easy for fungus to form.

now, when it comes to the meters. the one that never reads above 30 is broke. take that back.

the others varying within 13%... thats not much dude. you gotta remember, 100% humidity is SUBMERGED in water. 0% humidity doesnt exist really, other than a desert perhaps. what % are the other 4 meters reading at? are they all located in the same place? i ask becuase if they are reading say, 42, 46, 49, 55, but they are all in the same grow room, thats probably normal. if they are next to each other on the table, thats not.

either way, i went and bought a cheapo clock/date/humidity thing for about 20 bucks, and it seems to work fine, im usually at 50% humidity, and peaks around 70high, or 30 low, depending the weather, heat, etc...

i guess if you really want to know which is more accurate of the 5 sensors, watch the news and go outside with them? but 10% more or less wont make a big difference in your grow. honestly, id take them all back, buy 1 or 2 of the cheapo ones, and spend the money somewhere it might do more good, like nutes, or lighting.

otherwise, raise the humidity (buckets of water, uncovered) or lowering humidity (crank up the AC - make it colder). <-- thats all i do really when it comes to humidity... but i dont even do that. i got the AC to 70 degrees F, and i do preventative maintenance with a mold/fungus/rot killer, poured onto the soil before flowering, never had issues since. i keep my clones covered, and mist in there a bunch so i know those are humid.

dont stress it.

It doesnt control anything, but its a good datalogger, will record the vitals at specific intervals (every 1min, 5mins etc.) Max-Min, audible alarms at set limits....
Extech RH520

Thank you both for responding !

I guess I'll need to check the news more often, hang 'm outside for a few days and hope the weather-guy uses better sensors

While checking the sensors I placed them close to each other and logged data of all 5 continuously for a few days. The difference in readings (except those from the faulty one) aren't really a problem, I'm writing the program for the micro-controller and could correct the output in software.

I roughly know what plants need in what stage, but was simply wondering if there perhaps is a scientific way to test the accuracy and thus be able to correct the output in software as good as possible.

The Extech RH520 looks nice, I'm more or less building something like that, but with the possibility to vent air when humidity is too high and turn on an Ultrasonic fogger should the air become to dry. I'm busy with a lot more and Humidity will be a... routine in my homebuilt Grow-controller.

My controller being the sum of all parts, I there for also like every part to be as accurate as possible.